The invention concerns a procedure to make a fleece consisting of fibers with numerous hole structures extending over the entire cross-section, and a fleece manufactured according to this procedure.
One-layer or multilayer fleeces with hole structures extending over the entire cross-section are e.g. used for coverstock materials for articles of hygiene such as sanitary napkins and diapers, or for other textile or technical uses. The hole structures serve to quickly drain bodily fluids, tissue components and feces into the liquid-absorbing material of diapers, sanitary napkins, etc. Depending on the application, the fleeces can be single-layer or multilayer, whereby multilayer fleeces can be bonded with other sheet media such as films.
There are several prior-art procedures to introduce hole structures into a one-layer or multilayer fleece, whereby the common element of the prior-art procedures is that the hole structures are created in the finished fleece after bonding and especially thermobonding.
For example, a prior-art procedure in EP 0 687 757 A2 introduces hole structures into the bonded fleece by passing the fleece between heated stamps that are pressed together to melt holes in the bonded fleece. A similar prior-art procedure, a hot-needle punching procedure, is in U.S. Pat. No. 5,709,829.
The advantage of this procedure is that the bond of the fleece structure is held due to the melted edges that arise around the holes. A disadvantage is that the softness is negatively influenced by the relatively hard melted edges. A fleece obtained in this manner feels relatively hard and can be unpleasant to users.
In DE 34 16 004 A1, there is a prior-art process in which an unbonded fleece of thermoplastic fibers is fed to a calender roller arrangement, and the thermoplastic material is melted and displaced by pressure in the area of the holes by the calender roller arrangement. This produces a liquid bump at the edge of the holes to form a bonded grid to stabilize and fix the remaining fleece sheet. A hard melted edge is specifically created to reinforce the fleece sheet which is positive for the strength of the fleece sheet, but is disadvantageous due to the hardness of the melted edges.
In another prior-art procedure, the hole structures are created by (cold) stamping/cutting the fibers out of the bonded fleece. Such procedures have the advantage that hard stamped or melted edges do not arise, and materials obtained in this manner are soft. A disadvantage is that this procedure can only be done when the fleece is conveyed at a slow speed. In addition, the fibers are shortened along the holes which decreases the strength of the fleece.
A disadvantage of the cited procedures is that material is unnecessarily destroyed or wasted by hot and cold stamping or burning.
In another prior-art procedure in EP 0 214 608 A2, the fleece is manufactured and the hole structures are created by two rollers between which the fleece is guided. One roller has numerous heated needles, and the other roller has corresponding holes to receive the needles of the first roller. The needles purportedly displace the fibers while forming the hole structures and simultaneously form recesses around the hole structures, and they seal the edges of the hold structures by melting the fibers. In this procedure, the fibers are not shortened or destroyed, however hard melted edges arise that negatively influence the softness. In addition, it is involved and expensive to introduce hole structures after the fleece is thermobonded.
The problem of the invention is therefore to create a procedure that enables professionals to manufacture a fleece with hole structures that feels soft, the bond of the fibers is not weakened by introducing hole structures, the procedure can be done without waste, and it is simple and economical.
This problem is solved with a procedure of the initially-cited type that has the features of patent claim 1.
According to the invention, the fibers are randomly deposited on a screen belt to form a fibrous web in a first step of a procedure to create a fleece made of fibers with numerous hole structures extending over the entire cross-section of the fleece. In a second step, the fibrous web is transported to a hole-structure-creating machine; in a third step, the hole structures are created by mechanically displacing the fibers. The displacement of the fibers does not influence their mechanical and chemical structure. In a fourth step, the fibrous web with the hole structures is bonded in a bonding unit to form a fleece.
The invention is therefore based on the surprising knowledge that, to generate hole structures, it is sufficient to displace the fibers that cover the area of the holes to be formed and compress the fibers in this area and/or the neighboring area without having to destroy or impair the fibrous web in the area of the holes to be formed and/or its general appearance. In brief, the fibers of the fibrous web are reoriented in the area of the hole structures or diverted from their prior course in the procedure according to the invention before manufacturing the fleece by bonding and possibly thermobonding without requiring a heat treatment or simultaneous compression.
Suitable fibers or filaments for creating a fleece by the procedure according to the invention are any fibers or filaments suitable to form fleeces according to the various procedures, especially staple fibers, endless filaments, and bicomponent fibers and filaments. In particular, staple fibers are highly suitable.
It is particularly advantageous that no unnecessary waste or lost material arises, that the fibers are not shortened or destroyed in the area of the hole structures, and that the softness of the finished fleece is very good, and that no additional hardening at the edge of the hole structures impairs the softness of the finished fleece.
Such a solution has not been pursed to date since in particular in a prior-art process in EP 0 214 608 A2 it is assumed that the fibers would tend to return to their original position after being displaced due to the return effect which would eliminate the created hole structures. It was surprisingly shown that this return effect is irrelevant in the procedure according to the invention.
Before the third step, the fibrous web can be bonded to one or more fleeces and/or with another sheet medium such as a film.
In addition, the danger of the fibers springing back can be advantageously countered by feeding the fibrous web directly to the bonding unit after creating the hole structure. In such a bonding unit, e.g. a calender roller arrangement, the fibrous web is compressed to create the finished fleece and, in an advantageous embodiment of the invention, it is simultaneously thermobonded. A very short path is desirable so that the hole structure is not lost while the fleece is being transported from the hole-structure-creating unit to the bonding unit.
In another advantageous embodiment of the invention, the fibrous web is prebonded before the third step so that the tensile strength of the prebonded fibrous web is 0.1 to 75% and especially 50% of the tensile strength of the bonded fleece.
The unbonded fibrous web is more-or-less held by a few widely-spaced bonding points or by applying pressure and/or heat. This provides a certain amount of mechanical stability to the fibrous web so that it can be transported faster to the hole-structure-creating unit. The faster speed enables faster manufacturing.
In an advantageous embodiment of the procedure, the fibers surrounding the hole structures are fixed before feeding the fibrous web to the bonding unit. This serves to prevent the hole structures from stretching while transporting the fibrous web with the hole structures. Fixing the fibers, i.e., slightly adhering the fibers around the hole structure can be done with suitable means such as by applying heat and/or pressure to the fibrous web, e.g. by smooth rollers.
In addition, the fourth step can be carried out with the hole-structure-creating unit directly after the third step. In this case, the hole structure-creating unit is simultaneously used for bonding.
In a practical embodiment of the invention, the hole-structure-creating unit has two elements with facing surfaces between which the fibrous web is guided, whereby the surface of a first element has numerous barbs facing the fibrous web, and whereby the surface of a second element has openings in which the barbs of the first surface can at least partially enter, whereby the fibers of the fibrous web below the barbs are displaced without being destroyed when the barbs sink into the openings and the hole structures are formed.
In an advantageous embodiment of the invention, the openings of the second surface communicate with a source for a vacuum or pressure such as a blower so that fibers of the fibrous web in the area of the openings are sucked into or blown out of the openings. By sucking the fibers into the openings of the second surface, such a blower can support the nondestructive displacement of the fibers to form the hole structures, and the blower can blow the fibrous web with the hole structures away from the second surface to gently prevent potential adhesion of the fibrous web to the second surface after creating the hole structures.
The channels and openings of the vacuum source can shaped and dimensioned so that the fibers to be deformed or reoriented that are sucked into the openings and channel of the vacuum source are not caught.
In another advantageous embodiment of the invention, the first element is a roller. In practical embodiments of the invention, the roller has a diameter of 100-500 mm. Such a roller can be advantageous when a relatively fast production speed is to be attained.
In an alternate embodiment of the invention, the first element is a raising and lowering plate. Such a plate that can create discontinuous hole structures can be advantageous when the fibers are to be slowly and carefully displaced.
In practical embodiments of the invention, the barbs of the first element are conical or have an involuted shape or an ogival cross-section, whereby the barbs can have a practical height of 0.5-5 mm. Various shapes, sizes and heights of the barbs are used depending on the requirements, of the fleece to be created that can be single-layer multilayer fleece, e.g. a SMS fleece or a combination of fleece and other sheet media.
In another practical embodiment of the invention, the second element is a perforated belt. The fibrous web to be treated can be placed on such a perforated belt and transported to the first element where the barbs of the first element penetrate through the fibrous web into the holes of the perforated belt. Alternately, the second element can be calender roller. A calender roller would also be used as the second element.
In another practical embodiment of the invention, a fleece created by the procedure according to the invention has hole structures with a diameter of 0.5-5 mm, the bonding surface is 3-40% of the fleece surface, and the number of bonding points is 20-120 per square centimeter. Such a number of bonding points and a corresponding diameter of hole structures ensures a sufficient number of bonding points at the edge of the hole structures, and this fixes the hole structure so that the displaced filaments around the hole structures after hardening and thermobonding no longer return to their original position.